1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and a method for forming a resist pattern.
2. Description of the Related Art
There is a strong demand for a photoelectric conversion device having a high sensitivity. As a method that satisfies the demand, there is a method for forming a photoelectric conversion section to a position deep in a silicon substrate. According to this method, an impurity needs to be implanted to the position that is deeper than ever. Therefore, an ultrahigh energy implantation machine that can perform ion implantation to a silicon substrate with energy higher than 1 MeV has been promoted for practical use.
On the other hand, in order to perform ion implantation to a specific position on a silicon substrate, a well-known mask with a resist is used. The material of this mask needs to have at least a sufficient ion stopping ability against implantation energy. Ordinarily, a mask material for stopping the implantation energy needs to be formed so as to have a larger thickness as the implantation energy is higher. Particularly, when ion implantation with the above-described ultrahigh energy is performed, a mask material needs to be formed so as to have a larger thickness in order to satisfy a sufficient ion stopping ability as a mask material.
Japanese Patent Laid-Open No. 2002-217123 discloses that, when boron ion implantation energy is 4 MeV, the implantation depth is about 3 μm and a mask material needs to have a thickness of about 7 μm for ensuring the stopping ability as a mask material. It is furthermore disclosed that, when boron ion implantation energy is 5 MeV, the implantation depth is about 5 μm and a mask material needs to have a thickness of about 10 μm for ensuring the stopping ability as a mask material. In order to form a mask material having a sufficient ion stopping ability, Japanese Patent Laid-Open No. 2002-217123 discloses a method for forming a silicon layer having a thickness that is larger than 10 μm as a mask material.
Furthermore, as an alternative method, there is a method in which a photoresist is used as a mask material and formed so as to have a large thickness. For example, a method is known for stacking resists to form a mask material, which as well makes it possible for the thickness of the mask material to be large. The method for stacking resists is known from Japanese Patent Laid-Open No. 2006-73611.